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Influence of molecular coherence on surface viscosity.

Choi SQ, Kim K, Fellows CM, Cao KD, Lin B, Lee KY, Squires TM, Zasadzinski JA - Langmuir (2014)

Bottom Line: Adding small fractions of cholesterol decreases the interfacial viscosity of dipalmitoylphosphatidylcholine (DPPC) monolayers by an order of magnitude per wt %.Cholesterol significantly reduces the coherence area of the crystals as well as the interfacial viscosity.The extent of molecular coherence appears to be a fundamental factor in determining surface viscosity in ordered monolayers.

View Article: PubMed Central - PubMed

Affiliation: Chemical Engineering and Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States.

ABSTRACT
Adding small fractions of cholesterol decreases the interfacial viscosity of dipalmitoylphosphatidylcholine (DPPC) monolayers by an order of magnitude per wt %. Grazing incidence X-ray diffraction shows that cholesterol at these small fractions does not mix ideally with DPPC but rather induces nanophase separated structures of an ordered, primarily DPPC phase bordered by a line-active, disordered, mixed DPPC-cholesterol phase. We propose that the free area in the classic Cohen and Turnbull model of viscosity is inversely proportional to the number of molecules in the coherence area, or product of the two coherence lengths. Cholesterol significantly reduces the coherence area of the crystals as well as the interfacial viscosity. Using this free area collapses the surface viscosity data for all surface pressures and cholesterol fractions to a universal logarithmic relation. The extent of molecular coherence appears to be a fundamental factor in determining surface viscosity in ordered monolayers.

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Molecular tiltangle measured from the monolayer normal, θ,decreases in the same manner with increasing cholesterol fractionas with increasing surface pressure (over this range of θ, sinθtilt ∼ θtilt; to convertto degrees of tilt, θ° = 180(θtilt/π)).Black symbols −20 mN/m surface pressure, Open symbols −30mN/m and Gray symbols −40 mN/m. With some scatter, the tiltdecreases with increasing cholesterol fraction. This linear relationshipbetween d11 and θ is the same forchanges in cholesterol fraction and surface pressure, which suggeststhat the local alkane packing of DPPC does not change with added cholesterol,but that both surface pressure and cholesterol act to decrease themismatch between the lipid headgroup and tailgroup area in the sameway.
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fig4: Molecular tiltangle measured from the monolayer normal, θ,decreases in the same manner with increasing cholesterol fractionas with increasing surface pressure (over this range of θ, sinθtilt ∼ θtilt; to convertto degrees of tilt, θ° = 180(θtilt/π)).Black symbols −20 mN/m surface pressure, Open symbols −30mN/m and Gray symbols −40 mN/m. With some scatter, the tiltdecreases with increasing cholesterol fraction. This linear relationshipbetween d11 and θ is the same forchanges in cholesterol fraction and surface pressure, which suggeststhat the local alkane packing of DPPC does not change with added cholesterol,but that both surface pressure and cholesterol act to decrease themismatch between the lipid headgroup and tailgroup area in the sameway.

Mentions: Figure 3A shows that, at a fixed surfacepressure, adding Chol decreases d11 whileFigure 3B shows that d02 remains constant. For pure DPPC, d11 decreases from 4.79 to 4.58 Å as the surface pressureincreases from 20 to 40 mN/m; d02 is constantat 4.30 Å (Table 1). Cholesterol and surfacepressure influence the lattice in a similar way; the same linear relationshipbetween d11 and the tilt angle θholds over the range of surface pressures and cholesterol fractionsexamined (Figure 4). θ decreases withincreasing surface pressure, and with some scatter, increasing cholesterolfraction from 35° for pure DPPC at 20 mN/m to 18° for 7 mol % Chol at 40 mN/m. This change in tilt causesa decrease in the area per DPPC molecule at the air–water interfacefrom 49.9 ± 1 to 43.9 ± 1 Å2.


Influence of molecular coherence on surface viscosity.

Choi SQ, Kim K, Fellows CM, Cao KD, Lin B, Lee KY, Squires TM, Zasadzinski JA - Langmuir (2014)

Molecular tiltangle measured from the monolayer normal, θ,decreases in the same manner with increasing cholesterol fractionas with increasing surface pressure (over this range of θ, sinθtilt ∼ θtilt; to convertto degrees of tilt, θ° = 180(θtilt/π)).Black symbols −20 mN/m surface pressure, Open symbols −30mN/m and Gray symbols −40 mN/m. With some scatter, the tiltdecreases with increasing cholesterol fraction. This linear relationshipbetween d11 and θ is the same forchanges in cholesterol fraction and surface pressure, which suggeststhat the local alkane packing of DPPC does not change with added cholesterol,but that both surface pressure and cholesterol act to decrease themismatch between the lipid headgroup and tailgroup area in the sameway.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4334248&req=5

fig4: Molecular tiltangle measured from the monolayer normal, θ,decreases in the same manner with increasing cholesterol fractionas with increasing surface pressure (over this range of θ, sinθtilt ∼ θtilt; to convertto degrees of tilt, θ° = 180(θtilt/π)).Black symbols −20 mN/m surface pressure, Open symbols −30mN/m and Gray symbols −40 mN/m. With some scatter, the tiltdecreases with increasing cholesterol fraction. This linear relationshipbetween d11 and θ is the same forchanges in cholesterol fraction and surface pressure, which suggeststhat the local alkane packing of DPPC does not change with added cholesterol,but that both surface pressure and cholesterol act to decrease themismatch between the lipid headgroup and tailgroup area in the sameway.
Mentions: Figure 3A shows that, at a fixed surfacepressure, adding Chol decreases d11 whileFigure 3B shows that d02 remains constant. For pure DPPC, d11 decreases from 4.79 to 4.58 Å as the surface pressureincreases from 20 to 40 mN/m; d02 is constantat 4.30 Å (Table 1). Cholesterol and surfacepressure influence the lattice in a similar way; the same linear relationshipbetween d11 and the tilt angle θholds over the range of surface pressures and cholesterol fractionsexamined (Figure 4). θ decreases withincreasing surface pressure, and with some scatter, increasing cholesterolfraction from 35° for pure DPPC at 20 mN/m to 18° for 7 mol % Chol at 40 mN/m. This change in tilt causesa decrease in the area per DPPC molecule at the air–water interfacefrom 49.9 ± 1 to 43.9 ± 1 Å2.

Bottom Line: Adding small fractions of cholesterol decreases the interfacial viscosity of dipalmitoylphosphatidylcholine (DPPC) monolayers by an order of magnitude per wt %.Cholesterol significantly reduces the coherence area of the crystals as well as the interfacial viscosity.The extent of molecular coherence appears to be a fundamental factor in determining surface viscosity in ordered monolayers.

View Article: PubMed Central - PubMed

Affiliation: Chemical Engineering and Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States.

ABSTRACT
Adding small fractions of cholesterol decreases the interfacial viscosity of dipalmitoylphosphatidylcholine (DPPC) monolayers by an order of magnitude per wt %. Grazing incidence X-ray diffraction shows that cholesterol at these small fractions does not mix ideally with DPPC but rather induces nanophase separated structures of an ordered, primarily DPPC phase bordered by a line-active, disordered, mixed DPPC-cholesterol phase. We propose that the free area in the classic Cohen and Turnbull model of viscosity is inversely proportional to the number of molecules in the coherence area, or product of the two coherence lengths. Cholesterol significantly reduces the coherence area of the crystals as well as the interfacial viscosity. Using this free area collapses the surface viscosity data for all surface pressures and cholesterol fractions to a universal logarithmic relation. The extent of molecular coherence appears to be a fundamental factor in determining surface viscosity in ordered monolayers.

Show MeSH